ID: nht74-1.46

DATE: 11/05/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Midland-Ross Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to Midland-Ross' October 8, 1974, clarification of its February 8, 1974, petition for an amendment of S5.1.2.1 and S5.2.1.2 of Standard No. 121, Air brake systems, that would establish separate air reservoir volume requirements for several brake chamber types generally available in the air brake component market. You point out that Midland-Ross was referring to chamber stroke and not chamber diameter as the chamber dimension which could affect the safety of a brake system. You also requested that we adopt SAE Standard J10b instead of J10a as our specification of a reservoir that "withstands" certain internal hydrostatic pressure.

In our denial of your petition, we did understand your point that additional stroke could be discouraged by a reservoir capacity requirement based on chamber size at maximum travel of the piston or diaphragm. We found that the stopping distance requirements in effect mandate the installation of high performance components, and we do not anticipate a safety problem. If a safety problem does arise in the future, we would consider a modification of S5.1.2.1 and S5.2.1.2.

SAE Standard No. J10b is identical to J10a in its requirement that no rupture or permanent circumferential deformation of the reservoir exceed one percent. Therefore, for purposes of S5.1.2.2 and S5.2.1.3, we are adopting SAE J10b as our specification of "withstand" until we undertake further rulemaking.

Yours truly,

ATTACH.

POWER CONTROLS DIVISION Midland-Ross Corporation

October 8, 1974

James B. Gregory -- Administrator, U.S. Department of Transportation, National Highway Traffic Safety Adm.

Dear Mr. Gregory:

Subject: N40-30 (TWH)

Thank you for your response to our petition dated February 8, 1974 in regard to Section S5.1.2.1 and S5.2.1.2 of Standard 121 Air Brake Systems. We feel that our petition may not have been clear in regard to use of small volume chambers which apparently led to your misinterpreting our concern. We also believe you may have referred to the incorrect SAE Standard regarding air reservoirs.

In regard to our petition for clarification of air reservoir required volumes, we made mention of the fact that "current reservoir volume requirement based on maximum displacement encourages the use of small volume chambers". By this statement we did not imply smaller diameter chambers but shorter stroke chambers. It is quite easily determined that little chamber stroke is required if the foundation brakes are carefully adjusted with minimum liner to drum clearance. A chamber with 1.5" stroke could be adequate and will meet all of the standard's requirements. If a vehicle manufacturer would elect to go with this short stroke, he could reduce reservoir capacity by 25%. However, there would be very little safety factor to allow for drum expansion and liner wear. It is this condition of which we are concerned and feel it is wrong to penalize the vehicle manufacturer by requiring them to have larger reservoirs when they attempt to provide this additional safety advantage. We ask that you again review this matter and adopt one of the recommended changes to S5.1.2.1 and S5.2.1.2 as stated in our petition.

In the last paragraph of your response you mention the NHTSA has adopted the SAE Standard No. J10a in regard to the definition of "withstand". We assume you intended to refer to SAE Standard J10b and would appreciate your concurrence with this assumption.

Sincerely,

M. J. Denholm -- Director of Engineering

ID: nht74-1.47

DATE: 11/12/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Oshkosh

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your October 8, 1974, question whether a front axle automatic pressure limiting valve may be removed during the burnish procedure to permit effective burnish of the front brakes.

The answer to your question appears in Notice 6 to Docket 74-10 in response to a similar inquiry from International Harvester. A copy of that notice is enclosed for your information. It amends S6.1.8.1 to require that any automatic pressure limiting valve be in use except in the case where the temperature of the hottest brake on a rear axle exceeds the temperature of the hottest brake on a front axle by more than 125 degrees F. A bypassed valve is reconnected if the temperature of the hottest brake on a front axle exceeds the temperature of the hottest brake on a rear axle by 100 degrees F.

Yours truly,

Enclosure

ATTACH.

OSHKOSH TRUCK CORPORATION

October 9, 1974

Richard Dyson -- U.S. Dept. of Transportation, National Highway Traffic Safety Administration

Subject: 49 CFR Part 571, FMVSS 121 - Air Brake Systems

Dear Mr. Dyson:

Per Federal Bureau of Motor Carrier Safety Regulations, Part 393, Section 393.48, use of automatic devices for reducing front wheel brake effort is permitted on vehicles complying to FMVSS 121.

With the automatic pressure reduction valve in the front axle, Oshkosh Truck Corporation has found that during burnishing of some vehicles per Section 6.1.8.1 of FMVSS 121, the rear brakes reach 500 degrees F, much earlier than the front axle brakes because of the automatic reduction of brake force to the front axle and, therefore, effective burnishing of the front brakes is not achieved.

Please advise if the automatic device to reduce the front wheel brake force can be removed during the burnishing procedure.

Very truly yours,

P. K. Kamath -- Sr. Safety Engineer

ID: nht74-1.48

DATE: 05/23/74

FROM: AUTHOR UNAVAILABLE; L. R. Schneider; NHTSA

TO: The Flxible Company

TITLE: FMVSS INTERPRETATION

ID: nht74-1.49

DATE: 05/10/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Superior Trailer Works

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your April 22, 1974, question concerning the certification responsibility of a small manufacturer of trailers that must conform to Standard No. 121, Air brake systems. You ask if road testing of any or all vehicles produced would be necessary to satisfy the requirements.

A manufacturer must "exercise due care" in certifying that the vehicles manufactured by him comply with the applicable standards (National Traffic and Motor Vehicle Safety Act of 1966, @ 108(b)(2), 15 U.S.C. @ 1392(b)(2)). What constitutes due care in a particular case depends on all relevant facts, including such things as the time to elapse before a new effective date, the availability of test equipment to small manufacturers, the limitations of current technology, and above all the diligence evidenced by the manufacturer.

A small manufacturer of standard and custom trailers might fulfill his due care responsibility to assure that each of his trailers is capable of meeting the standard in several ways. For example, he could establish categories of models which share a common brake and axle system and certify them all on the basis of tests on the most adverse configuration in the category. Calculations should be written down in such a case to establish that reasonable care was taken in these decisions.

Alternatively, joint testing might be undertaken with a trade association or with a major supplier of brake and axle components. In the case of standard models, you might be able to rely on the supplier's warranty of his products' capacities.

Neither of these methods would require road testing of each vehicle manufactured, nor would every model have to be road tested. A manufacturer must simply satisfy himself that the trailer is capable of meeting the stopping performance requirements if it were tested by the NHTSA.

Yours truly,

ATTACH.

April 22, 1974

National Highway Traffic Safety Administration Attn: James B. Gregory, Administrator

Gentlemen:

We are a small trailer manufacturing firm currently producing approximately 100 trailers per year. These trailers are predominantly standard models (with some variations in body length and height), however, we also manufacture some custom trailers, principally low beds.

We do not manufacture brakes or axles or air system components, instead we purchase a complete axle-brake assembly and the air components, and assemble them into a trailer chassis. Under the Motor Vehicle Safety Standard 121 we will, of course, install components that meet the new requirements.

We are in the process of determining all the changes that we will be required to make under MVSS 121 and would appreciate clarification of the following:

1. Will we be required to road test complete trailers or will the inclusion of all certified components satify the requirements of the law?

2. If road testing of the complete trailer is required, is it required of every trailer produced, or would the test of a single prototype of a standard model be sufficient for all other trailers of the same model?

3. What road testing would be required for custom trailers that vary widely in length, width, height, capacity, etc.?

We have contacted several California trailer manufacturers, and they are in the same position that we find ourselves, i.e., no testing facilities of our own and without knowledge of any independent testing facility offering such a service. The size of the facilities required would make it all but impossible for any but a very large business firm to construct a special facility.

We are including some literature that will show the variations in equipment that we manufacture.

Your earliest possible comments would be greatly appreciated.

Very truly yours,

SUPERIOR TRAILER WORKS Charles R. Richards -- President

ID: nht74-1.5

DATE: 09/19/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: U. S. Technical Research Corporation

TITLE: FMVSS INTERPRETATION

TEXT:

NOA-30 (ZTV) Sep 19 1974

Mr. Bernard Belier U.S. Resident Engineer for Citroen, S.A. U.S. Technical Research Corporation 801 Second Avenue New York, New York 10017

Dear Mr. Belier:

This is in further reply to the petition of November 16, 1973, by Citroen, S. A. for rulemaking to amend Motor Vehicle Safety Standard No. 105-75, Hydraulic Brake Systems.

The petition has been thoroughly reviewed by engineering and legal staff personnel of this agency. Before a recommendation is made to the Administrator on the merits of your petition, we request that you furnish further information to us.

First of all, NHTSA is interested in obtaining any available data which will support the contention that the Citroen central power braking system provides a level of safety equivalent to a fully split system with indefinite residual failure mode performance such as is currently required by FMVSS 105-75. Do the highway accident statistics provide such support? Is the incidence of accidents occurring to Citroen vehicles attributable in whole or part to brake failures significantly different from the norm for other European passenger cars? Can it be demonstrated that when failures of the service brakes do occur in emergency situations, drivers are able to adjust their behavior patterns sufficiently quicly to bring the vehicles to a safe stop using the hand operated emergency brakes?

We wuld also like Citroen to provide data to substantiate that the "emergency" system can meet the deceleration requirement of 10 fpsps. What are Citroen's views on an appropriate burnish procedure for testing the emergency braking system? In addition to this, can the 10 fpsps deceleration requirement be achieved using the service brakes with a subsystem accumulator depleted?

Finally, we request data on the costs and leadtime required for Citroen to convert the single central power system to a dual, or full split system.

Yours truly,

Richard B. Dyson Acting Chief Counsel

cc: Maurice Clavel Assistant to the President S.A. Automobiles Citroen

ID: nht74-1.50

DATE: 07/11/74

FROM: AUTHOR UNAVAILABLE; Armstrong for R. L. Carter; NHTSA

TO: Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your May 10, 1974, request for interpetation of the volume requirements for service brake chambers in S5.2.1.2 and S5.1.2.1 of Standard No. 121, Air Brake System:

S5.1.2.1 The combined volume of all service reservoirs and supply reservoirs shall be at least twelve times the combined volume of all service brake chambers at maximum travel of the pistons or diaphragms.

You also requested that reservoir volume be based on manufacturer "rated volume" based on the designed volume of the reservoir.

In testing for compliance with S5.1.2.1 and S5.2.1.2, the NHTSA will accept a manufacturer's published "rated volume" of the brake chamber with the piston or diaphragm at maximum travel. This means that the manufacturer may specify the full stroke of the piston or diaphragm and compute the "rated volume" based on the designed volume of the chamber and the full stroke he has established. This volume may be somewhat larger than "nominal brake chamber displacement" which does not necessarily account for the void ahead of the relaxed diaphragm or piston, the so-called "prefill volume." This volume must be included because it must be pressurized along with the displaced volume.

In the absence of manufacturer's published ratings, the NHTSA will measure the brake chamber volume with the push rod at maximum stroke.

With regard to air reservoir volumes, the NHTSA will determine the volume of reservoirs by actual measurement. As a practical matter air reservoirs are simple structures whose volumes are relatively easy to measure.

Sincerely yours,

ATTACH.

Bendix

Heavy Vehicle Systems Group

Chief Counsel -- National Highway Traffic Safety Administration

May 10, 1974

Subject: Title 49 CFR, Part 571, Motor Vehicle Safety Standard No. 121, Air Brake Systems

Dear Sir:

Concern has arisen in the motor vehicle industry relative to the matter of brake chamber and reservoir volumes as set forth in Section 5.1.2.1, of the subject standard which provides:

"The combined volume of all service reservoirs and supply reservoirs shall be at least twelve times the combined volume of all service brake chambers at maximum travel of the pistons or diaphragms."

The question posed is: How will the sizing be verified for compliance purposes? Hence, an interpretation of Section 5.1.2.1 is requested.

Historically, the Industry has used the "nominal" or rated full stroke of brake actuators, in determining available stroke. In practice, it was understood that the nominal or rated full stroke is all that can be counted on to provide braking. (The recommended readjustment stroke followed by the Industry has been from 3/8 to 3/4 inch less than the "rated full stroke" depending upon actuator size.) Further, SAE recommended Practice J813, "Automotive Air Brake Reservoir Volume" does not go into any detail relating to strokes, tolerances, etc. of the various components involved in the actuation of a foundation brake.

The design of a braking system requires that a component, such as an actuator, which is called upon to give a specified stroke must have its own dimensions and tolerances so designated that its "minimum" travel provisions are those required for the system. To use the actuator's maximum stroke, taking into account tolerance stack up, as the basis for sizing a reservoir, appears to be unreasonable and would not increase the safety of the vehicle. (The maximum possible stroke is, of course, not available in every actuator and thus cannot be counted on for braking.)

It is therefore recommended that NHTSA give favorable consideration to an interpretation of Section 5.1.2.1 to provide that the brake chamber volume be specified at the advertised nominal or rated full stroke of the brake chamber. This volume can be determined by a manufacturer and precludes the necessity of adding additional reservoir volume to compensate for theoretical tolerances that in all likelihood will never become cumulative in the system.

An analogous situation exists with reservoirs. Because of the profusion of sizes and special configurations (different sizes and quantities of ferrules, and a variety of lengths and diameters) the minimum volume determined by physically filling several reservoirs of each configuration to measure the exact volume does not appear to add any reasonable degree of accuracy or safety.

Therefore, it is also recommended that the reservoir volumes be certified based on a "rated volume" produced by calculation using the actual nominal Engineering drawing dimensions. Ferrules would be ignored in the calculations as being insignificant and at any rate generally a "plus" for volume.

We solicit your comments on these matters and would be happy to discuss our recommendations with you if you feel that additional information is necessary.

Very truly yours,

R. W. Hildebrandt -- Group Director of Engineering

ID: nht74-1.6

DATE: 09/11/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: International Harvester

TITLE: FMVSS INTERPRETATION

TEXT:

SEP 11 1974

Mr. K. W. Berner Manager Component Design & Development International Harvester Truck Division Engineering 2911 Meyer Road Fort Wayne, Indiana 46803

Dear Mr. Berner:

This is in reply to your letter of August 13, 1974, to Dr. Gregory asking for confirmation of your interpretation of S5.3.1(b) of Motor Vehicle Safety Standard No. 105.

Paragraph S5.3.1(b) states that an indicator lamp shall be ?????? whenever there is "A drop in the level of brake fluid in a master cylinder reservoir to less than . . . one-fourth of the fluid reservoir capacity in any reservoir compartment ...." This will confirm that the lamp must activate whenever the fluid in any compartment is less than one-fourth the capacity of that compartment, rather than one-fourth the total capacity of the reservoir regardless of the number of compartments.

Yours truly,

Richard B. Dyson Acting Chief Counsel

ID: nht74-1.7

DATE: 12/18/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: The Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT:

Dec 18 1974 N40-30 (TWH)

Mr. J. R. Farron Group Director of Engineering The Bendix Corporation 401 Bendix Drive P. 0. Box 4001 South Bend, Indiana 46634

Dear Mr. Farron:

This responds to your undated letter which requests a determination that the Bendix "Hydro-boost" qualifies as a brake power assist unit" as that term is defined in Standard No. 105-75. You describe the unit as designed with a "push through" cabability in both the "normal" and "failed power" operating conditions, and with an accumulator that permits low pedal effort for a limited number of brake applications after a power failure has occurred.

The following definitions distinguish a "Brake power assist unit" from a "Brake power unit":

"Brake power assist unit" means a device installed in a hydraulic brake system that reduces the operator effort required to actuate the system, and that if inoperative does not prevent the operator from braking the vehicle by a continued application of muscular force on the service brake control.

"Brake power unit" means a device installed in a brake system that provides the energy required to actuate the brakes, either directly or indirectly through an auxiliary device, with the operator action consisting only of modulating the energy application level.

In the preaamble to Notice 8 of Docket No. 70-27, we made the further clarification that the capabilities of the unit in the "failed power" condition determine whether it is a brake power assist unit. A copy of this discussion is enclosed. Because the Bendix "Hydro--boost" in the "failed power" condition does not prevent the operator from braking the vehicle by a continued application of muscular force on the service brake control (i.e.. with "push through" capability), it qualifies as a brake power assist unit under the definitions of Standard No. 105-75.

Yours truly,

Original Signed By

Richard B. Dyson Acting Chief Counsel

Enclosure SECURITY=000

ID: nht74-1.8

DATE: 10/16/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Volkswagen of America, Inc.

TITLE: FMVSS INTERPRETATION

TEXT:

OCT 16 1974 NOA-30 (ZTV)

Mr. Joseph W. Kennebeck, Manager Emissions, Safety & Development Volkswagen of America, Inc. Englewood Cliffs, N. J. 07632

Dear Mr. Kennebeck:

This is in reply to your letter of September 24, 1974. You informed us that Volkswagen intends to introduce a new model, the Rabbit, in January 1975 that meets all requirements of Standard No.105-75 except S5.3.1.(b), requiring a brake fluid reservoir capacity indicator, which it will meet as of September 1, 1975. You also informed us that "one version of the Rabbit which meets FMVSS 105-75 exceeds the currently required preburnish check permissible pedal force." You therefore asked for an "interpretation of whether the Volkswagen Rabbit could comply with FMVSS 105-75 except for S5.3.1.(b) prior to September 1975, in lieu of complying with FMVSS 105 in effect up to that time."

In our view, the fact that the Rabbit exceeds the maximum specified preburnish check pedal force does not by itself indicate a failure to comply with existing Standard No. 105. Paragraph S4.1 of Standard No. 105 requires the performance ability of a passenger car service brake system to be "not less than that described in Section D of Society of Automotive Engineers Recommended Practice J937, 'Service Brake System Performance Requirements - Passenger Cars', June 1966." and tested in accordance with SAE Recommended Practice J843c, 'Brake System Road Test Code - Passenger Cars', June 1966." Section D of J937, Preburnish check, subreferences "SAE J843, Section C item 1".

The subreferenced item says that the purpose of the preburnish check is "to allow for a general check of instrumentation, brakes, and vehicle function," rather than a test of the effectiveness of the service brake system. Thus the preburnish check is not actually a test requirement. Although the distinction between test requirements, conditions and procedures is not made in the SAE materials incorporated into Standard No. 105, the successor Standard No. 105-75 distinguishes the three. It makes brake burnish part of the test procedure and sequence. Burnishing appears in the test procedure section, S7.4, and Table I, showing test requirements and corresponding procedures, does not relate it to any of the requirements of S5.

A manufacturer's certification covers only the performance requirements of the standard, and is his representation that if testing is conducted in the manner the standard specifies, the vehicle will meet those requirements. Therefore, no "waiver" of Standard No. 105-75 or amendment to Standard No. 105 appears necessary for Volkswagen to certify that the Rabbit complies with Standard No. 105, assuming, of course, that it meets all actual performance requirements of that standard.

Yours truly,

Original Signed By

Richard B. Dyson Acting Chief Counsel

ID: nht74-1.9

DATE: 03/15/74

FROM: AUTHOR UNAVAILABLE; J. B. Gregory; NHTSA

TO: General Motors Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This is in further reply to your letter of November 19, 1974, petitioning the NHTSA to amend Part 567, Certification (@ 567.4(f)), to allow the use of certification labels on which the lettering is embossed or engraved without regard to whether it contrasts with its background.

The NHTSA has decided that your petition should be denied. Our experience has been that certain types of engraving, those that are stencil-typed or stamped, are difficult to read without color contrast. The NHTSA considers it essential that certification labels be readable under all lighting conditions, and has not found embossing or engraving to produce by themselves sufficiently readable lettering for these labels. Of course, there is no prohibition against embossing or engraving if the finished lettering contrasts with its background.

We appreciate your point that Standard No. 105a accepts embossed or engraved lettering on the master cylinder reservoir label without requiring a color contrast. We are presently considering amending Standard No. 105a to eliminate this discrepancy.